The present application relates to an optical recording medium and a production method therefor, and a sputtering target and production method therefor. In particular, it relates to an optical recording medium such as a recordable blu-ray disk (BD-R) and a production method therefor, and a sputtering target suitable for use in production of such an optical recording medium and a production method therefor.
Recently, in the field of data recording, research and development on and commercialization of optical data recording technologies have seen rapid advancement. With the optical data recording technology, data can be recorded on and reproduced from an optical recording medium in a noncontact manner. The technology also has an advantage that it is adoptable to various forms of data recording, such as recordable, read only, and rewritable-type data, recording. In this respect, the technology can contribute to creating bulk; files at low cost and is adoptable to a wide variety of usages ranging from industrial to commercial.
Increasing the storage capacity of an optical recording medium (optical disk) for enabling various types of optical recording technology has been mainly achieved by decreasing the spot size at a focal plane through decreasing the wavelength of a laser beam, i.e. a light source used for recording and reproducing data, and using an objective lens with a high numerical aperture (NA). For example, for a compact disc (CD) having a storage capacity of 650 MB, a 780 nm laser beam and an NA 0.45 objective lens are used. For a digital versatile disk read only memory (DVD-ROM) having a storage capacity of 4.7 GB, a 650 nm laser beam and an NA 0.6 objective lens are used.
For a next generation optical disk system, an optical recording medium (optical disk) constituted by a substrate, an optical recording layer on the substrate, and a thin light-transmitting layer about 0.1 mm in thickness on the optical recording layer is used. A laser beam is applied to the optical recording layer from the light-transmitting layer side. Use of a laser beam having a wavelength of 450 nm or less and an objective lens with an NA of 0.78 or more enables a high storage capacity of 25 GB or more. How data is recorded on or read from the optical recording medium (optical medium) is illustrated in a schematic diagram of FIG. 1A. FIG. 1B is a cross-sectional view of this optical recording medium (optical disk), and FIGS. 1C and 1D are each an enlarged partial cross-sectional view showing a part of the cross-section of the optical recording medium (optical disk) shown in FIG. 1B.
An optical recording medium (optical disk) 10 includes a substrate (disk substrate) 20 about 1.1 mm in thickness composed of for example, a polycarbonate (PC) resin and having a featured main surface in which a recess 21 is formed, and an optical layer 33 formed along the featured surface that includes the recess 21. The optical recording medium 10 is of a phase change type and includes an optical recording multilayer structure 30 constituted by, for example, an incident-side protective film 34, the optical recording layer 33, and a reflective-side protective film 32. The reflective-side protective film 32 is located at the substrate side. A light-transmitting layer 41 having a thickness of for example, 0.1 mm is disposed on the optical recording layer 33 (in particular, on the optical recording multilayer structure 30).
Data is recorded or reproduced on the optical recording medium 10 by using an objective lens 12 having an NA of 0.78 or more (e.g. NA=0.85) and applying a laser beam having a wavelength of 450 nm or less (e.g., 380 nm to 420 nm) from the light-transmitting layer side so that the laser beam is focused on the optical recording layer 33. In reproducing the recorded data, feedback light reflected by the optical recording layer 33 is received by a photo receptor (not shown), particular signals are generated in a signal processing circuit, and reproduced signals can be obtained.
The optical recording layer 33 has features formed by the recess 21 in the surface of the substrate 20. The recess 21 is, for example, formed as a spiral continuous groove or circular grooves at predetermined pitches. The track regions are defined by these features. The recess in the features defining the track regions are called “groove” and a protrusion in the features defining the track regions is called “land”. Either the land or the groove is used as recording regions. Note that the storage capacity can be further increased by employing a land-groove recording technology that enables data recording on both the land and groove.
It has been reported that a non-stoichiometric mixture of a metalloid, namely, tellurium oxide, and palladium (Pd) (TeOxPd, wherein 0<x<2) can be used as the material for the optical recording layer 33 of the phase-change optical recording medium 10 (e.g. refer to Japanese Unexamined Patent Application Publication No. 61-068296). Data is recorded on an optical recording layer 33 composed of such a material on the basis of the following principle: the laser beam applied to the optical recording layer 33 melts the optical recording layer 33 and then as the optical recording layer 33 cools, phase separation between tellurium oxide and palladium occurs and changes the optical constant, based on which data is recorded. In other words, since the reflectance of the optical recording layer 33 changes between before and after irradiation with the laser beam, data can be reproduced by detecting the differences in reflectance.
Japanese Patent No. 3638152 describes an optical data recording medium and production method therefor, a method for recording and reproducing optical data, and a device for recording and reproducing optical data. In this patent, the optical data recording medium includes a transparent substrate and a data layer on the transparent substrate, the data layer containing at least Te, O, and atom M (wherein M is at least one element selected from the group consisting of metal elements, metalloid elements, and semiconductor elements). This data layer contains 40 atom % or more and 60 atom % or less of O, 2 atom % or more and 25 atom % or less of atom M, and 15 atom % or more and 58 atom % or less of Te, and has a thickness of 10 nm or more and 70 nm or less.